Control of organic deposition in slurry heaters in potash crystallizer circuit

ABSTRACT

IN THE PRODUCTION OF POTASH FROM AQUEOUS SLURRIES OF ORES SUCH AS SYLVITE IN THEIR TRANSIT THROUGH A POTASH CRYSTALLIZATION CIRCUIT INCLUDING SLURRY HEATERS WHICH RECEIVE THE SLURRY FROM A FEED TANK CONNECTED TO THE REPULP TANKS, A DEPOSITION OF UNDESIRABLE DEPOSITS FROM MATERIAL EXISTING IN THE ORE OCCURS AS A COATING IN THESE SLURRY HEATERS WHICH MATERIALLY DECREASES HEAT TRANSFER THEREIN SO THAT IT IS NECESSARY VERY FREQUENTLY TO REMOVE THE SLURRY HEATERS FOR CLEANING AND TO SUBSTITUTE SPARE HEATERS, RESULTING IN ECONOMIC LOSS BY VIRTUE OF DOWNTIME, LABOR AND DUPLICATION OF EQUIPMENT WITH RESULTANT INCREASED PRODUCTION COST. THIS IS AVOIDED BY ADJUSTING OR ELEVATING THE PH VALUE OF THE CRYSTALLIZER LIQUOR SLURRY FEED STREAM IN THE REPULP TANK THAT FEEDS THE SLURRY HEATER FEED TANK TO RANGE FROM ABOUT 9.0 TO 10.0, WHICH RESULTS IN SUPPRESSING FORMATION OF UNDESIRABLE DEPOSITS IN THE SLURRY HEATERS AND ELSEWHERE. SUBSEQUENTLY, THE RETURNING BRINE STREAM FLOWING TO A HOT THICKENER IS ACIDIFIED TO REDUCE ITS PH VALUE TO NORMAL VALUE OF APPROXIMATELY 7.5 PRIOR TO RECYCLING.

s. M. NIELS ON 3,674,442 CONTROL OF ORGANIC DEPOSITION IN SLURRY HEATERS July 4, 1972 IN POTASH CRYSTALLIZER CIRCUIT Filed May 20, 1969 Q x3 2:; :33 1 22 22:2; Q u

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INVENTOR STEPHEN M. NIELSON TTORNEY United States Patent O 3,674,442 CONTROL OF ORGANIC DEPOSITION IN SLURRY HEATERS IN POTASH CRYSTALLIZER CIRCUIT Stephen M. Nielsen, Provo, Utah, assignor to Texas Gulf Sulphur Company, New York, N.Y. Filed May 20, 1969, Ser. No. 826,195 Int. Cl. Btlld 9/02; C01d 3/08; C23f US. Cl. 23-299 4 Claims ABSTRACT OF THE DISCLOSURE In the production of potash from aqueous slurries of ores such as sylvite in their transit through a potash crys tallization circuit including slurry heaters which receive the slurry from a feed tank connected to the repulp tanks, a deposition of undesirable deposits from material existing in the ore occurs as a coating in these slurry heaters which materially decreases heat transfer therein so that it is necessary very frequently to remove the slurry heaters for cleaning and to substitute spare heaters, resulting in economic loss by virtue of downtime, labor and duplication of equipment with resultant increased production cost. This is avoided by adjusting or elevating the pH value of the crystallizer liquor slurry feed stream in the repulp tank that feeds the slurry heater feed tank to range from about 9.0 to 10.0, which results in suppressing formation of undesirable deposits in the slurry heaters and elsewhere. Subsequently, the returning brine stream flowing to a hot thickener is acidified to reduce its pH value to normal value of approximately 7.5 prior to recycling.

BRIEF SUMMARY OF INVENTION In the preparation of potash from aqueous slurries of ores such as sylvite a crystallization circuit is used which includes slurry heaters which receive the slurry from a feed tank connected to the repulp tank. It has been found that during use, the slurry heaters become contaminated by deposition as a coating of undesirable deposits formed by constituents of the ore such as clay, gypsum, shale oil and hydraulic oil which are contained primarily in the ore. This material deposited from such constituents as a coating in the heaters decreases heat transfer in the slurry heaters materially so that the heaters on duty must be taken out of service and cleaned frequently, almost during every shift, and replaced by spare heaters. These undesired contaminating deposits also have created difficulties in the hot thickener flow and in the hot tails centrifuge. The time delays incident to substitution and cleaning of the slurry heaters and other apparatus in which the undesired deposition occurs are wasteful and also increase production costs.

Objects and features of the present invention are the elimination of such undesired deposition and consequent need for substitution and frequent cleaning of slurry heaters and other apparatus in the crystallization circuit, thus reducing production time and cost.

As a simple and effective solution for elimination or suppression of these undesired deposits, it has been found that elevations of the pH from normal value of about 7.5 of the feed from the repulp tank to the slurry heater feed tank and thus to the slurry heaters to 9.0 or above, by treatment of the feed with a pH increasing agent selected from the group consisting of sodium hydroxide, soda ash, potassium hydroxide, ammonium hydroxide, hydrated lime, sodium carbonate, aluminum hydroxide or a basic character amine such as Nalco (344L-7362) (containing ammonia it is believed) a product of Nalco Chemical Company, of Chicago, 111., Will result in ef- 3,674,442 Patented July 4, 1972 fective elimination or suppression of such undesired deposits in said heater and elsewhere in the system. Subsequently, the returning brine stream leaving the heaters and leach apparatus is restored to its normal pH by acidification as by the addition of concentrated HCl or formic acid or other acidic neutralizing agent.

Furthermore, these undesired deposits are found easier to handle in the hot bird and tails system because of the agent added to increase the pH of the feed slurry.

As a preferred material to increase pH caustic (NaOH) soda has been selected because of its compatability with the crystallizer process. Since saturation of NaCl is achieved in the hot thickener used to treat returning brine, the excess sodium ion will precipitate and no extraneous ions will be added to the crystallizer process. Also, the projected cost for treatment is only four to five cents per ton of product. However, due to the adverse elfect that high pH has on flotation, it is necessary to reduce the pH of the bleed stream returning to the slimes thickener as by said acidification.

The particular agents utilized to increase pH must be compatible with the chemistry of the potash producing circuit and, in addition, be economical to use. The basic character Nalco amine referred to, while also found effective in preventing such Waste deposition requires about 33 gallons per ton of product and is too costly. On the other hand, use of sodium hydroxide as the agent is found to be effective and to result in a cost of only about 4 to 5 cents per ton of product. Also, such hydroxide is compatible with the chemistry of the system involved.

Other objects and features of the invention, therefore, are control of pH and its elevation in the ore slurry feed in the feed system by adding a pH increasing agent that is compatible with the chemistry of the system and economical to use.

Further objects and features of the invention will become apparent from the following detailed description and the accompanying drawing, wherein the single figure shown is a schematic showing of a treatment system for ores containing such waste to produce potash and to eliminate deposition of such undesired deposits particularly on the walls of the slurry heaters of the system.

DETAILED DESCRIPTION As seen from the drawing, the crushed ore concentrate, slimes, or other sources of KCl is put intoa repulp tank and the slurry is delivered therefrom with addition thereto of brine. The agent for increasing the pH from normal value of about 7.5 to 9.0 or above is added to the liquor in the repulp tank using, for example, a Clarkson feeder to regulate the amount of additive agent introduced. The pH increased effluent from the repulp tank is then fed to a slurry heater feed tank, being tested in transit for pH and the feed of agent increased or reduced as needed to bring the pH value of the effluent from the repulp tank to about 9.3 or as an economical upper limit to about 10. From the slurry feed tank, the eflluent at proper elevated pH, e.g. 9.340 is fed to the slurry heater and the efiluent from the latter then is passed successively through several leach tanks and from thence the leach liquor is pumped to a hot thickener Where the brine is clarified by settling before being fed to crystallizers. On leaving the final leach tank, the leach liquor is treated to restore its pH to normal of about 7.5, e.g. by addition of a neutralizing material such as concentrated HCl or formic acid or other acidic neutralizing agent, pH sampling being effected between the pump and hot thickener to control the amount of acid introduced to an amount needed to lower the pH of the brine effluent to said normal value. It is found that the amount of such acidic agent necessary for such purposes is very small.

Example I Potash ore containing material whose deposition it is desired to eliminate or suppress and which analysis in one instance at least has been found to be about 80% organic material and to include gypsum, clay and oil is admixed with brine and fed to a repulp tank. A pH increasing agent, for example, a 50% solution of sodium hydroxide (NaOH) is added to the aqueous solution in the repulp tank until the normal 7.5 pH thereof is elevated to about 9.3 and up to an economic value of 10.0. The solution at said elevated pH is then fed to a slurry heater feed tank and thence to the slurry heater, being sampled enroute as to pH to insure that it lies at 9.0 or above.

The addition of this agent to increase the pH to said value range is found to be effective in substantially preventing undesired deposits from said material in the slurry heaters and elsewhere in the system. It is economical as the cost is but 4 to 5 cents per ton of product. It is also compatible with the crystallization system.

The efiiuent brine liquor from the slurry heater is fed to leach tanks and ultimately pumped to a hot thickener to clarify the brine and then to crystallizers. En route from the last leach tank an acidic neutralizing agent such as concentrated hydrochloric acid or formic acid is added to the brine to reduce its pH to normal 7.5.

The muds from the hot thickener are dewatered and discarded, the clear liquors overflowing the thickener are fed to crystallizers in which the K01 is crystallized, depleting such content in the brine. The brine is then recycled for mixture with fresh ore being fed to the repulp tank.

In preparation of the pH increasing agent 12 gallons of water per 100 lbs. of NaOH solids provides the requisite 50% solution of NaOH agent. Feed rate of this solution to effect required pH elevation is started at a maximum and adjusted as needed to elevate the pH to 9.3 by periodic or automatic sampling of the feed liquor entering the slurry heater feed tank. The amount of neutralizing acid requisite to restore pH to normal 7.5 is small and is regulated by sampling of the leach eflluent flowing to the hot thickener.

Example II The same procedure is followed as in Example I, substituting said Nalco 344-L-7362 for sodium hydroxide solution at the rate of approximately 33 gals/ ton of product to elevate and maintain the pH of the feed liquor to the slurry heater to at least 9.0. Unwanted deposits in the slurry heaters are substantially eliminated.

Example 111 The same procedure is followed as in Example 1, subtituting as the additive agent ammonium hydroxide solu tion in sutficient quantity to elevate the pH to at least 9.0 with results similar to the previous examples.

Example IV The same procedure is followed as in Example 1, substituting as the additive agent hydrated lime in suflicient quantity to elevate the pH to at least 9.0. Elimination or suppression of undesirable deposits in the slurry heaters are effected.

Example V The same procedure is followed as in Example I, substituting as the additive agent aluminum hydroxide in snflicient quantity to elevate the pH to at least 9.3. Similar results are achieved as in the other examples.

Example VI The same procedure is followed as in Example I, substituting as the additive agent sodium carbonate in sutlicient quantity to elevate the pH to at least 9.0. Similar results occur as in the other example.

4 Example VII The same procedure is followed as in Example I, substituting as the additive agent soda ash in sufiicient quantity to elevate the pH to at least 9.0. Similar results occur as in the other example.

Example VIII The same procedure is followed as in Example 1, substituting as the additive agent potassium hydroxide in sufficient quantity to elevate the pH to at least 9.0. Similar results occur as in the other example.

In all examples, while the elevation of pH is to at least 9.0 it can go higher to 10.0 or more since excess agent additive works equally well. However, since a pH of 9.3 is adequate, to eliminate or suppress unwanted deposits in the slurry heaters and elsewhere and because some buffering occurs in the feed, elevation of pH above 10 requires a greater proportion of added pH increasing agent and becomes uneconomical in practice. Thus, a pH range increase to from 9.3 to 10 is deemed the practical and preferred range.

While specific examples of practicing the invention have been disclosed, variations in detail within the scope of the appended claims are possible and are contemplated. There is no intention of limitation to the exact abstract and disclosure herein presented.

What is claimed is:

1. In the treatment of potash containing material including crushed ore concentrate, slimes and other sources of KCl and also containing as contaminants clay, gypsum, shale oil and hydraulic oil, said contaminants being predominantly of organic content and wherein a brine slurry of said material with all said contaminants therein is fed through a slurry heater in a crystallizer circuit and in which heater all said contaminants in the slurry tend to form undesirable deposits as coatings on said heater, the prevention of deposition of all said contaminants as coatings in said heater including the step of preparing a brine slurry of the said material and all said contaminants thereof in a repulp tank, the step of elevating the pH value of the brine slurry in said repulp tank from its normal value of approximately 7.5 to at least 9 by addition to such slurry of a pH increasing agent selected from the group consisting of sodium hydroxide, soda ash, potassium hydroxide, ammonium hydroxide, aluminum hydroxide and hydrated lime, feeding the pH value increased slurry from said repulp tank to said slurry heater, sampling the slurry fed from said repulp tank to said heater in advance of its entry into said heater, and adding additional of said pH increasing agent thereto during its feed to said heater to maintain the pH value of the fed slurry at at least 9 which value is sufiicient to prevent deposition of all said undesired contaminants including the organic content as coatings on said heater, removing leach liquor as an efiiuent from the slurry heater and reducing the pH value of said efliuent leach liquor from the slurry heater to said normal value of about 7.5 by addition to said efiluent leach liquor of an acidic neutralizing agent and then recycling said leach liquor at its said normal pH value via a hot thickener and crystallizer to said repulp tank.

2. That improvement according to claim 1, wherein the elevation of pH value is to from 9.0 to 10.

3. That improvement according to claim 1, wherein said pH increasing agent is a 50% sodium hydroxide solution and said neutralizing agent is I-ICl.

4. In the treatment of potash containing material including crushed ore concentrate, slimes and other sources of KCl and also containing as contaminants clay, gypsum, shale oil and hydraulic oil, said contaminants having about organic content and wherein a brine slurry of said material with all said contaminants therein is fed through a slurry heater in a crystallizer circuit and in which heater all said contaminants in the slurry tend to form undesirable deposits as coatings on said heater, the

prevention of deposition of all said contaminants as coatings in said heater including the step of preparing a brine slurry of the said material and all said contaminants thereof in a repulp tank, the step of elevating the pH value of the brine slurry in said repulp tank from its normal value of approximately 7.5 to at least 9 by addition to such slurry of a pH increasing agent selected from the group consisting of sodium hydroxide, soda ash, potassium hydroxide, ammonium hydroxide, aluminum hydroxide and hydrated lime, feeding the pH value increased slurry from said repulp tank to said slurry heater, sampling the slurry fed from said repulp tank to said heater in advance of its entry into said heater, and adding additional of said pH increasing agent thereto during its feed to said heater to maintain the pH value of the fed slurry at at least 9 which value is sufficient to prevent deposition of all said undesired contaminants including the organic content as coatings on said heater, removing leach liquor as an effluent from the slurry heater and reducing the pH value of said efiluent leach liquor from the slurry heater to said normal value of about 7.5 by addition to said effluent leach liquor of an acidic neutralizing agent selected from the group consisting of hydrochloric and formic acids and then recycling said leach liquor at its said normal pH value via a hot thickener and crystallizer to said repulp tank.

References Cited UNITED STATES PATENTS OTHER REFERENCES Cyanamid, Bulletin on Cyanamer, p. 35 Antiprecipitant, October 1965, pp. 1-5.

Salutsky; 1st Inter. Sympo. on Water Desal, Oct. 3, 1965, SWD/95, page 1.

NORMAN YUDKOFF, Primary Examiner O S. J. EMERY, Assistant Examiner US. Cl. X.R.

23302, 312 A H; l59--DIG. l3; 203--7 

